Endoparasites in Dogs: Properly Recognizing and Treating Worms and Giardia

Dogs love exploring the world with all their senses. However, invisible dangers can hide in grass, puddles, parks, or during contact with other dogs. Internal parasites, such as worms and protozoa, are common in dogs and can affect their health without always causing obvious symptoms.

Many dog owners are unsure how best to protect their pet. Yet an untreated parasite infection can lead to digestive problems, weight loss, or more serious health complications. Some parasites may even pose a risk to humans.

In this guide, discover the most common internal parasites in dogs, the symptoms they can cause, and how to protect your dog effectively.

What are endoparasites in dogs?

Endoparasites are parasites that live inside (from the Greek "endo") a host animal and feed on its nutrients or blood. In dogs, they usually nest in the gastrointestinal tract, but sometimes also in organs like the lungs or heart.

The most important endoparasites in dogs include worms (e.g., roundworms, hookworms, tapeworms, and heartworms) as well as microscopic protozoa (like Giardia or Coccidia). Since these parasites often remain completely unnoticed for a long time, solid knowledge about prevention and diagnosis is crucial.

How do you recognize an infestation? The most important symptoms

From a medical perspective, the signs of a parasitic infestation are often non-specific at first. A mild infestation frequently remains completely asymptomatic in adult, healthy dogs. Nevertheless, there are some warning signs that you, as an attentive dog owner, should definitely pay attention to:

The most common internal parasites at a glance

1. Roundworms

These worms are a major problem, especially for young dogs, as they are often transmitted from the mother to the puppies via breast milk or in the womb. They deprive the dog of essential nutrients for growth and can severely damage the intestinal mucosa.

2. Hookworms

Hookworms are blood-sucking parasites that attach themselves to the intestinal mucosa. Infection occurs either through ingestion from the environment or – which is particularly insidious – through the active penetration of larvae across intact skin, usually on the paws. A severe infestation can lead to dangerous anemia and bloody diarrhea.

3. Tapeworms

Tapeworms are usually transmitted by intermediate hosts. If your dog eats an infected mouse during a walk outside or accidentally swallows a flea during daily grooming, it can get infected very quickly.

4. Heartworms (Dirofilaria)

The "classic" heartworm is primarily a travel disease transmitted by infected mosquitoes in southern and eastern countries. The larvae migrate through the bloodstream and develop into adult worms that settle in the large blood vessels of the lungs and in the heart. An untreated infection leads to severe heart failure.

5. French Heartworms (Lungworms)

Despite its name, the French heartworm (Angiostrongylus vasorum) is actually a lungworm that is becoming increasingly common in our latitudes too. Dogs get infected when they intentionally or accidentally eat infected snails or slugs outside – often just chewing on a tuft of grass where a small snail was sitting is enough. The worms infect the blood vessels of the lungs and, in addition to coughing, can cause life-threatening blood clotting disorders.

6. Giardia: Stubborn protozoa

Giardia are highly resistant protozoa that commonly cause chronic, often foul-smelling diarrhea in dogs. Infection mainly occurs through contaminated water or feces, and this parasite is very common. In cases of recurrent diarrhea, it is recommended to test your dog for giardiasis.
Giardia can survive for long periods in the environment in the form of cysts, which increases the risk of reinfection. If the test is positive, strict hygiene measures (cleaning and disinfecting the environment) are essential.
For more information, please refer to our dedicated article.

Treatment and Prevention: How to protect your dog

How often should a dog be dewormed or tested for parasites? To protect your dog and your own family, the following approaches have proven effective:

1. Regular fecal examinations with modern PCR tests

Instead of routinely deworming your dog "blindly", a prior fecal examination is increasingly recommended. A state-of-the-art and extremely reliable approach here are pezz PCR tests.

• The advantage of the PCR method: In contrast to the classic observation under the microscope, the laboratory searches directly for the DNA of the parasites during a PCR test. This makes the test extremely accurate, even if the worms are not shedding eggs at that moment. The tests also reliably cover Giardia or lungworms.
• The application: You simply collect stool samples on three consecutive days using the test kit and conveniently send them to the laboratory. In the event of a positive result, you can treat targetedly, while at the same time sparing your dog's intestinal flora if the test is negative.

2. Veterinary recommendations for deworming frequency

Whether you opt for prophylactic deworming or regular tests, the frequency depends heavily on your dog's lifestyle:

• Dogs with normal risk: For a typical family dog walking in the city or on normal walking paths, we recommend testing or deworming at least four times a year (every three months).
• Dogs with high risk: Does your dog like to eat feces outside, hunt mice, or live in a household with toddlers or immunocompromised people? Then, from a medical perspective, we advise a monthly examination or deworming.

Additional hygiene measures in everyday life